This invention relates to a capacitive angle sensor of a type including a rotor fixedly connected for rotation with a sensor shaft and a stator fixed on a sensor housing, the rotor and stator lying in planes parallel to each other.
Because they occupy small structural spaces and fastening points thereof are positioned close to each other, diameters of angle-sensor rotors must be small. So that capacitance of precision capacitors thereof is sufficiently large, a slight separation of the capacitor plates is required. Vibrations and large fluctuations in temperature of a combustion engine, which affect such sensors, make it necessary to structure the sensors to be vibration resistant and non-warping. No partial change in the separation of the capacitor plates arising from warping forces can arise. A dielectric thereof may not change, but must remain sufficiently constant at least within a measuring period. So that a capacitive sensor operates without contact, a rotor signal is not connected with electronics via a wiper, but rather via a series connected decoupling capacitor.
German patent document (DE 43 13 886 A1) discloses a capacitive position and angle sensor that comprises two electrode supports that move with respect to each other. On each electrode support, electrodes, that form sensor capacitance, on the one hand, and coupling capacitance, on the other hand, are positioned opposite each other. At least one electrode of the coupling capacitance is coated with a wear-resistant metal-oxide passivation coating so that, upon assembly of the two electrode supports to form a sensor, this passivation coating assures a stable brace for the two movable electrode supports and at the same time includes an air dielectric.
German patent document (DE 43 22 750 A1) discloses a capacitive rotational angle sensor that includes a rotor disk that is fixedly connected for rotation with a sensor shaft and at least one stator disk fixed on a sensor housing, the two being arranged in parallel planes to each other and having electrode structures on their sides facing each other. A dielectric coating comprised of a PTFE lubricating varnish is applied to the electrodes, which form a rotational-angle-dependent capacitance, for providing an electrode separation. Both the stator disk and the rotor disk are positioned centrally on the sensor shaft within the sensor housing.
German patent document (DE 44 14 529 C2) discloses a rotational angle sensor of a capacitance type. The rotational angle sensor disclosed therein has two fixed electrodes divided by intermediate spaces, as well as a third, rotatably-mounted electrode that is also divided by an intermediate space.
United States patent document (U.S. Pat. No. 5,681,990) discloses a capacitive sensor for determining a setting position of a throttle valve. This sensor has a movable electrode plate and an output electrode. Conducting and insulating segments are placed on the movable electrode plate facing the output electrode. A rotor is located between the two electrodes, on a circumference of which a collar is applied for ensuring a defined distance between the electrodes within the sensor.
It is an object of this invention to provide a capacitive angle sensor in which, despite vibration and influences of temperature, a rotor is held in a non-warping manner and with an even spacing to a stator.
According to principles of this invention, a parallel rotor and stator of a capacitive angle sensor are structured as ceramic plates having electrode structures on their sides facing away from each other, with the ceramic plates forming a dielectric.